MXPA00000023A

MXPA00000023A - Methods for inhibiting the polymerization of vinyl monomers

Info

Publication number: MXPA00000023A
Application number: MXPA/A/2000/000023A
Authority: MX
Inventors: Graciela B Arhancet
Original assignee: Betzdearborn Inc
Priority date: 1997-07-01
Filing date: 2000-01-03
Publication date: 2001-03-05

Abstract

An alpha-tocopherol is diclosed as a polymerization inhibitor effective against vinyl monomer polymerization. Alpha-tocopherol was found to inhibit polymerization of acrylonitrile and diolefines such as isoprene and butadiene. Alpha-tocopherol was found to interact synergistically with hydroquinone in inhibiting polymerization of acrylonitrile.

Description

METHODS TO INHIBIT THE POLYMERIZATION OF VINYL MONOMERS FIELD OF THE INVENTION The present invention relates to methods for inhibiting the polymerization of vinyl monomers. More specifically, the present invention relates to the method for inhibiting the polymerization of vinyl monomers during processing and storage of vinyl monomers.

BACKGROUND OF THE INVENTION Polymerizable vinyl monomers polymerize undesirably during the different stages of manufacturing, processing, handling, storage and use thereof. It is well known that vinyl monomers polymerize easily and that this polymerization increases with concurrent increases in temperature. Common industrial methods for producing vinyl monomers include different purification processes, including distillation to remove impurities. Unfortunately, purification operations carried out at elevated temperatures * give rise to an increased undesired polymerization rate. Polymerization, such as thermal polymerization during the monomer purification process, results not only in the loss of the desired final monomer product, but also in the loss of production efficiency caused by the formation or agglomeration of the polymer in the polymer. processing equipment. In operations that require heat, this agglomeration adversely affects heat transfer efficiency. Vinyl monomers can be polymerized when left in storage tanks and during transport at temperatures as low as room temperature. To prevent this polymerization from being carried out, vinyl monomers are often treated with polymerization inhibitors. To inhibit the uncontrolled polymerization of the vinyl monomers, different compositions and methods have been proposed. For example, the polymerization of acrylonitrile can be inhibited with phenothiazine, hydroquinone (HQ), methyl ether of hydroquinone (MEHQ), benzoquinone, methylene blue and combinations of hydroxyethyl and phenylalanine diamine [sic]. See, for example, U.S. Patent No. 4,720,566. The inhibition of the polymerization of isoprene can be obtained by the addition of tert-butylcatechol. { TBC). TBC is also used commercially to inhibit the polymerization during storage of butadiene and styrene.

U.S. Patent No. 4,561,124 discloses the use of vitamin E as an inhibitor against the premature initiation of polymerization in reactive systems capable of undergoing polymerization initiated by free radicals, whose system before and / or after the polymerization thereof is placed in tissue contact with a living body. The reactive composition of interest in U.S. Patent No. 4,561,124 are monocomponent or medical components and / or dental-medical adhesives, cements or fillers based on conventional monofunctional and / or polyfunctional olefinically unsaturated compounds, particularly acrylic acid and / or methacrylic acid or derivatives thereof. U.S. Patent No. 5,159,106 describes the use of a finely dispersed liquid phase containing inhibitors to stabilize reactive liquids in the production of (meth) acrylic acid. The liquid phase finely dispersed forms a continuous liquid film on the surfaces of the internal wall of the equipment. The inhibitors described include hydroquinone, sterically hindered hydroquinone such as di-tert-butylhydroquinone and sterically hindered phenolic compounds of the tocopherol type.

SUMMARY OF THE INVENTION The present invention has discovered that alpha-tocopherol (vitamin E) is highly effective against the polymerization of vinyl monomer under various conditions. In particular, it was found that alpha-tocopherol inhibits the polymerization of isoprene and acrylonitrile under accelerated conditions that simulate processing and storage conditions. It was also found that alpha-tocopherol interacts synergistically with hydroquinone in the inhibition of acrylonitrile polymerization under simulated storage and processing conditions.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to methods for inhibiting the polymerization of vinyl monomers, which consists of adding an effective inhibiting amount of alpha-tocopherol alone or in combination with hydroquinone. The alpha-tocopherol or combination of alpha-tocopherol and hydroquinone are effective in inhibiting the polymerization of vinyl monomers during processing, storage or transportation conditions. The present inventor anticipates that the methods of the present invention can inhibit the polymerization of vinyl monomers during processing thereof. These processing conditions, such as purification and distillation processes, usually employ heat and will often cause embedding of the monomer. The vinyl monomers of the present invention are characterized by a grouping CH2 = CH- and are highly reactive and polymerize easily. These include vinyl chloride, vinyl acetate and similar esters; styrene, methyl methacrylate and acrylonitrile as well as isoprene. For the purposes of the present invention, the term "effective amount" refers to the amount of alpha-tocopherol or combination of alpha-tocopherol and hydroquinone necessary to inhibit the polymerization of vinyl monomers. This amount may vary according to the conditions under which the ethylenically unsaturated monomer is subjected during storage and handling thereof. At higher temperatures and higher monomer contamination, larger amounts of the polymerization inhibiting compound are generally necessary. Preferably, the effective amount of alpha-tocopherol or the combination of alpha-tocopherol and hi-d-quinone added to the vinyl monomer is in the range from about 1 part to about 10,000 parts per million parts of the monomer. More preferably, the amount of alpha-tocopherol or the combination of alpha-tocopherol and hydroquinone added to the monomer is in the range of about 1 part to about 500 parts per million parts of the monomer. The ratio of aifa-tocopheri to hydroquinone can be in the range from about 1 to 9 to about 9 to 1. The preferred ratio is about 1 to 1. The alpha-tocopherol or the combination of alpha-tocopherol and hydroquinone can be added to the vinyl monomers as a dispersion or as a solution using a suitable liquid carrier or solvent. It is possible to use any solvent that is compatible with the treatment and the vinyl monomer. The invention will now be described with reference to different specific examples that are considered only as illustrative, and not as limiting the scope of the present invention.

EXAMPLES Tests were conducted to determine the effectiveness of the present invention in inhibiting the polymerization of vinyl monomers of isoprene and acrylonitrile. The tests were performed in a stainless steel pressure vessel (constructed in accordance with ASTM 252-88) adapted with a glass sample container and stopper, a rod, a pressure gauge with a continuous recorder and valves and accessories adequate. A solution of the vinyl monomer to be tested and the designed polymerization inhibition treatments were placed in the sample glass container and inside the pressure vessel. The vessel was closed, filled with oxygen at 100 psig and heated in a 100 ° C water bath. The pressure was recorded continuously until a point of inflection was reached in the pressure-time curve (ie the greater slope of the curve). The induction time was calculated as the time elapsed between the placement of the container in the bath and the point of inflection. The results of these tests are reported in the following.

Example I The procedure described above was employed with solutions of 10 milliliters of isoprene and 40 milliliters of heptene and the designed treatment. Table 1 summarizes the results.

Table 1 Treatment Dose (ppm) Induction time (min.) White 25 TBC 10 40 a-tocopherol 10 40 a-tocopherol 50 89 TBC is ter-butyl catechol The results demonstrate that the components of the present invention are effective in inhibiting the polymerization of vinyl monomers (isoprene) under approximate storage conditions. The commercially available TBC inhibitor demonstrated similar performance, but it is significantly more also toxic than the inventive material.

EXAMPLE II Non-inhibited acrylonitrile (10 milliliters) was placed in a 50 milliliter pressure glass tube adapted with a stopper. The desired treatment was added, the tube was closed and immersed in an oil bath at 110 ° C. Every 30 minutes the tubes were inspected for turbidity or the presence of polymer and the elapsed time was recorded. Tables 2 and 3 summarize the results, Table; 2 Treatment Dose (ppm) Induction time (min.) White 60 HQ 1 270 HQ 2.5 350 HQ 5 560 a-tocopherol 1 450 a-tocopherol 2.5 600 a-tocferferol 5 1300 Table 3 Treatment Dose (ppm) Induction time (min.) *** White 50 HQ 1 100 a-tocopherol 1 360 a-tocopherol / HQ 1 720 HQ is hydroquinone *** average of three processes These results demonstrate that the compounds of the present invention are effective in inhibiting the polymerization of vinyl monomers (acrylonitrile) under conditions approaching storage. The commercially available inhibitor, hydroquinone, proved to be less effective than the materials of the invention. In addition, a combination of the inventive material and hydroquinone exhibited synergistic activity. Although this invention has been described with respect to the specific embodiments thereof, it is evident that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The attached clauses and this invention, in general, should be considered to cover all these obvious forms and modifications that are within the true spirit and scope of the present invention.

Claims

1. A method for inhibiting the polymerization of unsaturated vinyl monomers during processing, storage and transport consists in adding to the vinyl monomers an amount effective to inhibit the polymerization of an alpha-tocopherol. The method of claim 1, wherein the alpha-tocopherol is added to the monomers in an amount in the range of from about 1 to about 10,000 parts per million parts of the monomer. The method of claim 1, wherein the alpha-tocopherol is added to the vinyl monomers in an amount in the range from about 1 to about 500 parts per million parts of the vinyl monomer. 4. The method of claim 3, wherein the vinyl monomer is acrylonitrile. 5. The method of claim 4, wherein the inhibiting amount of the polymerization of an alpha-tocopherol further contains hydroquinone. The method of claim 5, wherein the ratio alpha-tocopherol to hydroquinone is in the range from about 1 to 9 to about 9 to 1. 7. The method of claim 1, wherein the vinyl monomer is a diolefin selected from the group consisting of isoprene and butadiene. The method of claim 7, wherein the alpha-tocopherol is added to the vinyl monomers in an amount in the range of from about 1 to about 1,000 parts per million parts of the vinyl monomer. 9. The method of claim 7, wherein the vinyl monomer is exposed to oxygen atmospheres. 10. A method for inhibiting the polymerization of unsaturated vinyl monomers consists in adding to the unsaturated vinyl monomers an effective inhibiting amount of the polymerization of a combination of (a) an alpha-tocopherol and (b) hydroquinone. The method of claim 10, wherein the ratio of alpha-tocopherol to hydroquinone is in the range from about 1 to 9 to about 9 to 1. The method of claim 10, wherein the vinyl monomer is select from the group consisting of acrylonitrile and diolefins. The method of claim 12, wherein the diolefins are selected from the group consisting of isoprene and butadiene.